As electronic and electric devices are increasingly becoming more compact, more lightweight, or thinner, there is also a growing demand that electrochemical devices such as secondary batteries used as the power source for such devices be more compact, more lightweight, or thinner. For example, lithium secondary batteries are equipped with a roll-type electrode plate group that is obtained by laminating a positive electrode comprising a current collector and a positive electrode active material layer formed thereon and a negative electrode comprising a current collector and a negative electrode active material layer formed thereon, with a separator interposed there between, and winding the resultant trilaminar sheet. Alternatively, lithium secondary batteries are equipped with an electrode plate group having a layered structure that is obtained by folding the above-mentioned trilaminar sheet a plurality of times. Further, there has been proposed an electrode plate group that is obtained by alternately laminating a plurality of positive electrode sheets and a plurality of negative electrode sheets with a separator interposed there between so that the separator is folded in a zigzag manner between the positive electrode sheets and the negative electrode sheets (e.g., see Patent Document 1).
Meanwhile, to increase volume energy density, it has been proposed, for example, to laminate a positive electrode active material or negative electrode active material on a separator and forming a thin internal electrode layer (current collector) on the active material (e.g., see Patent Document 2). In this way, by reducing the thickness of the current collector and thus increasing volume energy density, it is possible to realize a thin, high-energy-density battery.
Further, to improve the output characteristics, reliability, and capacity of the battery, it has been proposed to use a current collector sheet composed of a resin sheet and a conductive layer of a predetermined pattern formed on each side thereof (e.g., see Patent Document 3).
Patent Document 1: Japanese Laid-Open Patent Publication No. 2002-329530
Patent Document 2: Japanese Laid-Open Patent Publication No. Hei 8-138726
Patent Document 3: Japanese Laid-Open Patent Publication No. 2004-253340